The present invention relates to a master cylinder for dual hydraulic brake circuits, with frontal sealing valves.
Master cylinders of this type usually consist of a cylinder having one end closed and the other open, with first and second pistons, preferably identical to each other, each sliding in a respective bore section of corresponding diameter formed inside the cylinder. First and second reaction springs are interposed respectively between the first and the second piston and between the closed end of the cylinder and the second piston, keeping both pistons in normal positions spaced furthest away from the closed end of the cylinder. In this way the pistons define with the internal walls of the cylinders two compression chambers each of which is in use of the master cylinder connected via appropriate passages and ducts to a respective reservoir and to respective brake actuator cylinders for the rear and front wheels of the vehicle. Each piston is further equipped with frontal valve means adapted, upon operating the brake pedal, to interrupt the communication between the compression chambers and the reservoirs, thus allowing the brake fluid in the compression chambers to be pressurised to operate the brake actuators.
In master cylinders of this type eventual wear or damage of the intermediate sealing gasket of the second piston nearer to the closed end of the cylinder, which ensures the sealing of the piston in the respective cylinder bore, cannot be noticed in any way and the master cylinder then functions as a common master cylinder for a single circuit so that further damage to any other part of the system then puts out of action the entire braking system. This results from the fact that, upon operating the brake pedal, the front sealing valves interrupt the communication with the reservoirs, so that the fluid can flow only from one compression chamber to the other without being able to flow into one of the reservoirs and raise the fluid level therein. Consequently it is impossible to adopt as a brake fault warning one of the signalling systems known for detecting such rises, for example a float system associated with the reservoirs.
An object of the present invention is to provide a master cylinder of the aforesaid type, which is free of the above mentioned disadvantages and in which any damage or deterioration of the intermediate sealing gasket abovementioned can be noticed immediately, while independence of the two brake circuits is ensured at all times.